Installation and method for producing and disaggregating synthesis gases from natural gas

ABSTRACT

What is described is a method and an installation for the simultaneous production of methanol synthesis gas, ammonia synthesis gas, carbon monoxide and carbon dioxide from natural gas, in which several plant elements (or plant units) are serially arranged one by one in one single production chain, whereat these elements comprise: a first reactor A, in which the natural gas is transformed under oxygen supply into a synthesis gas mixture comprised of carbon monoxide, carbon dioxide, hydrogen and steam (water vapour), a second reactor B, which allows to control the transformation of carbon monoxide into carbon dioxide, optionally a compressor C for compressing the generated gases, an absorber D for the absorption of carbon dioxide and for obtaining the carbon monoxide-hydrogen mixture used for methanol synthesis, a low-temperature separator E, in which ammonia synthesis gas is obtained by introducing liquid nitrogen, and in which simultaneously carbon monoxide, argon and methane are removed.

Subject of the invention is a plant and a method for the simultaneousproduction of synthesis gases like methanol synthesis gas, ammoniasynthesis gas, carbon monoxide and carbon dioxide by fractionating a gasmixture generated from natural gas.

For the production of methanol, ammonia, pure carbon monoxide, carbondioxide and other synthesis gases it is known to erect productionplants, in each of which in general only one of the afore mentionedgases can be produced [(2) and (3)]. Only methods for the simultaneousproduction of methanol and ammonia are already known from the Germanpublished patent application DE 33 36 649, the Japanese patentapplication JP 200 006 3115 and from the European patent 0 853 608. Atechnically important approach suitable for this aim comprises thetransformation of a naturally occurring natural gas into a synthesis gascontaining carbon monoxide, carbon dioxide and hydrogen as majorcomponents. Methods for the production of synthesis gas have beendescribed e.g. in the German published patent application DE 33 45 064and in the European patent application EP-A 0 999 178.

For economical reasons however, it would be extremely advantageous if itwas possible to perform a such complete fractionation of the componentsof a synthesis gas in one single production plant, that methanolsynthesis gas, ammonia synthesis gas, carbon monoxide and carbon dioxidecould be obtained in one single production chain in a highly pure formto be directly available for further chemical syntheses. Such a combinedgas fractionation plant would be particularly efficient not only forreason of the obtainable savings in consequence of increased productionoutputs, but also because several elements of the production plant—incontrast to a higher number of separate plants each of which is adaptedto just one single product—would be required only as a single specimen.A plant of this kind could be particularly economical if it was possibleto realise it in such a flexible manner, that one is allowed to adaptthe amounts of the different gases obtained from that plant to theactual needs.

It has now be been discovered, that these requirements can be fulfilledby a plant for the simultaneous production of methanol synthesis gas,ammonia synthesis gas, carbon monoxide and carbon dioxide from naturalgas, if the following plant elements (or plant units) are seriallyarranged one by one in one single production chain:

-   -   a first reactor A, in which the natural gas is transformed under        oxygen supply into a synthesis gas mixture comprised of carbon        monoxide, carbon dioxide, hydrogen and water,    -   a second reactor B, which allows to control the transformation        of carbon monoxide into carbon dioxide,    -   optionally a compressor C for compressing the generated gases,    -   an absorber D for the absorption of carbon dioxide and for        obtaining the carbon monoxide-hydrogen mixture used for methanol        synthesis,    -   a low-temperature separator E, in which ammonia synthesis gas is        obtained by introducing liquid nitrogen, and in which        simultaneously carbon monoxide, argon and methane are removed.

The reaction process is schematically depicted in the enclosed FIG. 1.

The first reactor A serves to produce synthesis gas and allows for thedesulphurization of the employed gas mixture, its saturation with steam(water vapour), the heating in a heater under catalytic degradation ofhigher hydrocarbons (longer chain hydrocarbons) into methane, thepartial oxidation with oxygen, and a cooling of the gas under theproduction of steam. Such a plant element, also designated as a CPoxreactor (catalytic partial oxidation), is frequently employed in theconstruction of plants and is described in literature (1). Itconstitutes a cylindrical vessel having vertically arranged, arcuatewalls. A burner or a mixer is provided in the upper part of the vessel,into which a naturally occurring natural gas mixed with steam, steamitself and oxygen are each introduced via separate feeding lines. Theburner or mixer supports a thorough mixing of these three gas streams inthe upper part of the vessel, in which the major portion of the partialoxidation is accomplished very quickly. The hot gases are then passedover a catalyst present in the bottom part of the vessel, where thetransformation of the natural gas is completed. The catalytic partialoxidation can be characterised by the following chemical reactionequations:

Steam is fed to the reactor A in such an amount, that one reaches amolar ratio of steam to non-oxidised hydrocarbons of 1.4 up to 3.0,preferably of 1.7. Oxygen is fed to the reactor A in an amount, that themolar ratio of oxygen to non-oxidised hydrocarbons is 0.45 up to 0.7,preferably 0.52. The exact amount of oxygen in practice is therebycontrolled, that the starting temperature of the gas mixture fromreactor A is adjusted to temperatures between 900 and 1050° C., ingeneral to 950° C. The purity of the oxygen supplied by the airseparation plant F (see FIG. 1) in general ranges between 90 and 99.5%,but usually is about 99.5%. The catalyst used in the reactor A is anickel oxide catalyst, e.g. a catalyst of the types G-31 E, G-90LDP orG-90B, which can be obtained from the Sud-Chemie AG, Munich, Germany.The transformation of the natural gas into a synthesis gas isaccomplished at a pressure of 20 to 100 bar, preferably at a pressure ofabout 40 bar. The reactor A is connected to a second reactor B, in whichthe generation of carbon dioxide from carbon monoxide can be controlledwhile simultaneously producing hydrogen. The reactor B however alsoprovides a bypass [3], via which the synthesis gas mixture produced inthe first reactor A can be entirely or partially guided past the reactorB, thus allowing to control the degree of transformation of the gasmixture. In the reactor B, the oxidation of carbon monoxide to carbondioxide is accomplished as a one- or two-step process with intermediatecooling in the presence of high temperature catalysts.

If there is no need or only a little need for carbon dioxide, thesynthesis gas obtained from reactor A is guided past the reactor B andis then, via line [4], immediately fed into a compressor C, which allowsto compress the generated gas mixture. Compressor C serves to compressthe gas generated in reactor A to a pressure between 60 and 100 bar, ingeneral to a pressure of 80 bar. However, if the pressure of the gaswithdrawn from reactor A is already over 40 bar, the use of a compressorcan be omitted. The compressor employed in this context is a well knowndevice as it is commonly used in many chemical plants.

Starting from the compressor C, the gas mixture is then fed to theabsorber D via line [5], whereat the absorber serves to remove thecarbon dioxide from the gas mixture. This may either be accomplished ina physical or chemical way. In a physical gas cleaning, the carbondioxide is absorbed by cold methanol or by cold glycol ether. In achemical washing, the absorption is preferably accomplished by analkanol amine, sodium carbonate or another alkaline substance.Preferably, the absorber D provides two reaction steps, whereat in thefirst reaction step a rough separation of the carbon dioxide isaccomplished, leading to a molar concentration between 1-10% by weight,calculated on the basis of the dry gas, preferably however it is aremoval of up to a concentration of 2.2% by weight. In the secondabsorption step, the remaining carbon dioxide is then removed, therebyreaching a molar concentration of less than 50 ppm, preferably of lessthan 10 ppm. The absorber D also comprises a means for a controlledreduction of the gas pressure of the absorbent in order to thereby allowfor a recovery of carbon dioxide. The absorber D moreover comprisesmeans for regenerating the absorbent by applying heat, means formaintaining a constant composition of the absorbent and also foradjusting the solvent's gas pressure to the process pressure. The carbondioxide recovered that way can be entirely or partially used forsubsequent syntheses, e.g. for the production of urea. Excess carbondioxide is discharged to the atmosphere. Several other methods forremoving the carbon dioxide are described in the references (2), (3) and(4).

The gas mixture, now being free from carbon dioxide, is then fed vialine [7] to the low temperature separator E, in which a partialcondensation and separation of carbon monoxide and hydrogen isaccomplished by introducing liquid nitrogen. This method is described indetail in the German patent application 102 26 210.1, which has beenfiled at the same date. In consequence, a methanol synthesis gas beingcomprised of carbon monoxide and hydrogen, is obtained. The purity ofthe carbon monoxide obtained from the low temperature separator E can befurther improved by a methane purification.

The carbon monoxide obtained in the low temperature separator E can alsobe fed to a plant for the production of acetic acid by a carbonylationof methanol.

Contaminations with methane or argon are as well removed by the nitrogenwashing in the low temperature separator E; these contaminations maythen be used as a fuel gas for the heat production in reactor A.

In the low temperature separator E, the gas is cooled off to atemperature in the range between −200° C. and −150° C. At thistemperature, the gas is subjected to a flash evaporation in one or moreevaporator drums, thereby separating hydrogen from carbon monoxide. Atfirst, the flash evaporations yield a liquid hydrogen, which is rich incarbon monoxide. The gaseous carbon monoxide gas is washed with liquidcarbon monoxide in order to purify the gas and to remove methane, afterwhich the carbon monoxide gas is reheated to room temperature. Thehydrogen is then passed through a second washing column, where it iswashed with liquid nitrogen in order to remove traces of carbonmonoxide, argon and methane. The molar ratio of hydrogen to nitrogen isthen adapted to a value of 3:1 in order to obtain a gas mixture beingsuitable for ammonia synthesis.

The low temperature separator E moreover comprises a molecular sieve inorder to remove traces of carbon dioxide already before the lowtemperature separation takes place, thus yielding a carbon dioxide-freesynthesis gas. The low temperature separator E as well is a known plantelement and is described in detail in reference (5).

The plant element F being depicted in FIG. 1 is a common air separationplant producing a stream of oxygen with a purity between 90 and 99.5%.The plant element F moreover provides nitrogen with a purity of over99.995%.

The gases obtained in the plant according to the invention and accordingto the afore mentioned methods are produced in a such highly pure form,that they can be used for subsequent chemical syntheses.

The efficiency of the plant according to the invention, here beingadapted to the production outputs given in the following, and the methodfor the fractionation of a synthesis gas to be accomplished therein, isillustrated by the following example:

-   a) It is intended to produce 4000 tons of methanol per day, a part    of which is employed for the production of acetic acid. The    synthesis of methanol requires a composition of the synthesis gas    with a stoichiometric number S_(n) of 2.05, a carbon dioxide    concentration in the range between 2 and 3% and a nitrogen    concentration of less than 0.5%. The stoichiometric number (S_(n))    is calculated according to the following formula:    $S_{n} = {\frac{\left( {\left\lbrack H_{2} \right\rbrack - \left\lbrack {CO}_{2} \right\rbrack} \right)}{\left( {\left\lbrack {CO}_{2} \right\rbrack + \lbrack{CO}\rbrack} \right)}.}$    In this formula, [H₂] [CO₂] and [CO₂] [CO] represent the molar    concentrations of hydrogen, carbon dioxide and carbon monoxide in    the synthesis gas;-   b) Simultaneously, one can yield synthesis gases for 1200 tons of    acetic acid per day from the same plant. The production of acetic    acid requires methanol and carbon monoxide with a purity of at least    98%;-   c) Furthermore, synthesis gases for 4000 tons of ammonia per day can    be obtained from the same plant, a part of which is used is used for    the production of urea. The production of ammonia requires a mixture    of hydrogen and nitrogen in a molar ratio of 3:1, whereat the gas    mixture must contain less than 10 ppm of oxygen.-   d) Finally one can moreover obtain synthesis gases for 6270 tons of    urea per day from the same plant. The production of urea requires    pure ammonia as well as carbon dioxide with a purity of more than    98.5%.

These requirements can be fulfilled by using the following procedure,whereat the composition of the individual gas streams is given in table1:

-   1. The raw synthesis gas produced from natural gas is generated in    the reactor A and adjusted to a pressure of about 45 bar. It leaves    reactor A with the composition [2];-   2. About 82% of the raw synthesis gases from reactor A are guided    past the reactor B as a gas stream [3], whereas 18% of the raw    synthesis gas are subjected to a controlled transformation of carbon    monoxide into carbon dioxide accomplished in reactor B. The gas    stream leaving the reactor B is then united with the gas stream [3]    in order to form a gas stream [4];-   3. The cooled and condensed gas stream [4] is then compressed to a    pressure of about 80 bar in the compressor C;-   4. The compressed gas is fed to the absorber D, from which about 43%    of the synthesis gas is withdrawn, when the carbon dioxide absorbent    reaches a mean degree of saturation and when the carbon dioxide    concentration is reduced to about 2.2%. The gas then has the    composition of the gas stream [6]. The remaining gas is subjected to    a second absorption during a carbon dioxide intensive purification,    whereat at carbon dioxide concentration of less than 10 ppm is    achieved. This gas is fed as a gas stream [7] into the low    temperature separator E.-   5. In the low temperature separator E, carbon monoxide is separated    from the synthesis gas, whereat the carbon monoxide is then utilized    as a gas stream [10] for acetic acid synthesis or as gas stream [11]    for ammonia synthesis or as a stream of residual gas (gas stream    [8]), whereat the gas stream 8 is united with the methanol synthesis    gas in a gas stream [9]. Contaminations of the synthesis gas like    methane, argon and carbon monoxide are employed as a fuel gas and    fed to the burner of reactor A;-   6. The carbon dioxide obtained from the absorber D is employed for    urea synthesis via the substance stream [15].

The above described fractionation of the synthesis gas into severalindividual fractions in one single plant is just one example for thenearly unlimited potential of supplying gas mixtures required forspecific chemical syntheses by means of combining the plant elementscontained in the plant according to the invention with chemicaltransformation methods. By means of suitable modifications andalterations of the individual plant elements and process steps it is aswell possible to obtain also specific gas mixtures from natural gas inone single plant, whereat these gas mixtures may be then e.g. beemployed for other important syntheses like the Fischer-Tropschsynthesis, the oxo-alcohol synthesis, the ethylene glycol synthesis andother processes.

REFERENCES

-   1. Hermann Göhna, “Concepts for Modern Methanol Plants”. Proceedings    of the 1997 World Methanol Conference, Tampa, Fla., USA (December    1997)-   2. “Gas Production”, Ulimans's Encyclopedia of Industrial Chemistry,    Vol. A12, VCH Verlagsgesellschaft mbh (1989)-   3. Max App “Ammonia, Methanol, Hydrogen, Carbon Monoxide, Modern    Production Technologies”. British Sulphur Publishing—a Division of    CRU Publishing Ltd., 31 Mount Pleasant, London WC1X 0AD. ISBN 1    873387 26 1 (published 1997)-   4. Emil Supp “How to produce Methanol from Coal”. Springer-Verlag    (1990)

5. W L E Davey “Cold Box for the Production of Multiple Products from aStream of Syngas”. German Patent Application No. ? (2002) (L1P13) TABLEI Gas stream 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Composition (% byvolume) Methane 95.4 1.64 1.64 2.39 2.39 2.41 2.47 5.67 2.89 0.57 0.60Ethane 3.91 Propane 0.03 Carbon 13.88 13.88 17.71 17.72 19.32 19.7385.41 29.96 98.19 <5 0.4 monoxide ppm Carbon 0.59 6.65 6.65 12.18 12.192.24 1.91 98.5 dioxide Argon 0.06 0.06 0.08 0.08 0.09 0.09 0.40 0.140.36 <150 0.40 0.50 0.01 ppm Hydrogen 44.56 44.56 67.42 67.47 75.9577.71 8.52 65.97 0.87 75.00 0.5 Nitrogen 0.08 0.02 0.02 0.02 0.02 25.0079.0 99.99 Oxygen 20.6 99.5 Water 33.18 33.18 0.19 0.11 Temp. 22 412 41240 41 36 36 36 36 36 36 22 36 36 32 (° C.) Pressure 23 39.6 39.6 37.279.3 77.8 77.8 76.3 76.3 5 76.3 1.0 45 55.0 1.2 (bar abs) Rate of 207820 668 483 482 121 147 63 185 24 168 1.058 208 154 192 flow (t/h)

1. Installation for the simultaneous production of methanol synthesisgas, ammonia synthesis gas, carbon monoxide and carbon dioxide fromnatural gas, characterised in that several plant elements are seriallyarranged one by one in one single production chain, whereat theseelements comprise: a first reactor A, in which the natural gas istransformed under oxygen supply into a synthesis gas mixture comprisedof carbon monoxide, carbon dioxide, hydrogen and steam (water vapour), asecond reactor B, which allows to control the transformation of carbonmonoxide into carbon dioxide, an absorber D for the absorption of carbondioxide and for obtaining the carbon monoxide-hydrogen mixture used formethanol synthesis, a low-temperature separator E, in which ammoniasynthesis gas is obtained by introducing liquid nitrogen, and in whichsimultaneously carbon monoxide, argon and methane are removed. 2.Installation according to claim 1, characterised in that a compressor Cis provided, in which the gases generated in reactors A and B can becompressed.
 3. Installation according to claim 1, characterised in thatthe reactor A exhibits feed lines for natural gas, steam and oxygen inorder to accomplish a catalytic partial oxidation of the natural gas. 4.Installation according to claim 1, characterised in that the secondreactor exhibits a bypass, via which the synthesis gas mixture obtainedin reactor A can be entirely or partially guided past said reactor B,thus allowing to control the degree of oxidation of the synthesis gasmixture, in particular the generation of carbon dioxide from carbonmonoxide.
 5. Installation according to claim 2, characterised in that acompressor C is provided, by which the gas pressure can be adjusted to avalue assuring the physical or chemical absorption of carbon dioxide inthe absorber D.
 6. Installation according to claim 1, characterised inthat the absorber D exhibits a feed line for the synthesis gas mixtureand discharge lines for the methanol synthesis gas being comprised ofcarbon monoxide and hydrogen, for carbon dioxide and for the synthesisgas being purified of carbon dioxide and as well as for gases beingsuitable for other syntheses and having the respective appropriatecompositions.
 7. Installation according to claim 1 characterised in thatthe low temperature separator E exhibits feed lines for the synthesisgas being purified of carbon dioxide and for liquid nitrogen anddischarge lines for the ammonia synthesis gas, for pure carbon monoxide,for a fuel gas containing methane, argon and carbon monoxide and for afluid containing carbon monoxide and hydrogen.
 8. Method for thesimultaneous production of methanol synthesis gas, ammonia synthesisgas, carbon monoxide and carbon dioxide from natural gas by introducingsteam (water vapour) and oxygen into a plant according to claim 1,characterised in that in the first reactor the molar ratio of steam tonon-oxidised hydrocarbons is 1.5 up to 3.0, preferably 1.7.
 9. Methodaccording to claim 8, characterised in that in the first reactor themolar ratio of oxygen to non-oxidised hydrocarbons is 0.45 up to 0.7,preferably 0.52.
 10. Method according to claim 8, characterised in thata catalyst containing nickel oxide is used for transforming the naturalgas into a synthesis gas.
 11. Method according to claim 8, characterisedin that for transforming the natural gas into a synthesis gas, apressure of 25 to 100 bar, preferably a pressure of about 40 bar, isused.
 12. Method according to claim 8, characterised in that for theoxidation of carbon monoxide to carbon dioxide in the second reactor B,a one- or two-step method with intermediate cooling in the presence ofhigh temperature catalysts is performed.
 13. Method according to claim8, characterised in that the synthesis gas produced in the reactors Aand B is adjusted by means of the compressor C to a pressure of 60 to100 bar, preferably of 80 bar.
 14. Method according to claim 8,characterised in that in the absorber D the carbon dioxide is separatedfrom the synthesis gas in one or more process steps in a chemical orphysical way.
 15. Method according to claim 8, characterised in that thesynthesis gas is cooled off to temperatures of −150° C. to −200° C. inthe separator by introducing liquid nitrogen and that thereby methane,argon and carbon monoxide are removed and that the remaining hydrogengas is mixed with nitrogen in a molar ratio of 3:1 in order to obtainammonia synthesis gas.